Effects of coral-derived organic matter on the growth of bacterioplankton and heterotrophic nanoflagellates

Abstract

Exudates derived from hermatypic corals were incubated with <2 µm filtered seawater containing heterotrophic bacteria and <10 µm filtered seawater containing bacteria and nanoflagellates (HNF) under dark conditions for 96 h to quantify the growth of both bacteria and HNF in response to coral-derived dissolved organic matter (DOM). The addition of coral-derived DOM caused significantly higher growth rates and production of bacteria and HNF compared to those in control seawater without coral exudates. During the incubation, HNF exhibited their peak in abundance 24–48 h after the peak abundance of bacteria. The growth efficiencies of both bacteria and HNF were significantly higher with coral-derived DOM, suggesting higher transfer efficiency from bacteria that is fueled by coral organic matter to HNF. Therefore, trophic transfer of coral-derived DOM from bacteria to HNF can contribute to efficient carbon flow through the microbial food web.

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Acknowledgements

The authors thank F. Azam (Scripps Institution of Oceanography) and two anonymous reviewers for critical reading and helpful comments on this manuscript; I. Mimura, N. Nakatomi, Y. Tadokoro and K. Ohtaka for their help in sampling or sample analysis; A. Tsugi and K. Nagamoto for providing temperature and light data; K. Okaji for providing modular roller apparatus; and staff at the Sesoko Station for supporting this research. This study was partially supported by Asahi Group Foundation, JSPS KAKENHI Grant (No. 26870916), and JSPS Fellowship for Research Abroad.